The present invention relates to articles produced by sintering and in particular to lightweight jewelry and decorative articles of novel appearance produced by sintering of spherical particles of precious metals.
Casting is generally the chosen method for production of jewelry from precious metals, such as karat gold, silver, and platinum, since creation of a three-dimensional object of complex shape from a metal is difficult unless the metal is melted.
Casting may be an extremely expensive method in the case of metals, which have a high melting point, such as platinum and titanium, necessitating heating of casting furnaces to extremely high temperatures
Sintering was originally developed as an alternative to casting from molten metal or forging at softening temperatures. Sintering involves welding together of small particles of metal by heating to a temperature below the melting point of the metal, under appropriate atmospheric conditions.
Sintering requires heating of the metal to a temperature corresponding to approximately 80% of its melting point. The bonding between atoms is the same as that produced by casting.
The driving force in sintering is decreasing surface energy. As the sintering proceeds, adjacent particles partially coalesce due to diffusion processes so that the total surface area decreases.
Sintering generally involves powder particles, which may be produced by gas-assisted atomization. In this method, the metal is first heated above its liquidation temperature. The molten metal then flows through a nozzle whereupon a high-pressure gas stream breaks up the metal into small droplets, which upon cooling become metal powders. Gas pressure can be adjusted to produce droplets having the required dimensions, with increased gas pressure producing finer droplets.
Standard sintering of metals involves compacting the particulate metal into a desired shape under substantial pressure then sintering to cause bonding of the particles. This produces an article of high structural strength.
In gravity or low pressure sintering, a mold is filled with uncompacted metal powder then heated to sintering temperature. Gravity sintering is carried out under conditions of atmospheric pressure. In low pressure sintering, the pressure applied is less than that at which deformation of spheres occurs. The result is a low-density article in which particles are generally more uniform in size than those of high-density articles.
U.S. Pat. No. 6,062,045 to West discloses a jewelry item and method of making same using powdered sinterable metal. The method involves sintering of hard metal into a blank, to which a precious metal may then be affixed. High pressure is used in the process, resulting in a solid blank of desired shape. The jewelry item produced is similar in appearance to items produced by casting methods, but is wear resistant.
Use of spherical particles of precious metal rather than powdered metal would give a unique appearance to the surface of the article produced by sintering, providing attractive and original items of jewelry and decorative objects. Such items would have a lower density than an equivalent cast item, making them lighter and more comfortable to wear, and enabling air flow between spheres.
Therefore, it would be desirable to economically provide items of jewelry and decorative objects from precious metals in which the final product has a unique and attractive appearance and lower density than similar items produced by casting.
Accordingly, it is an object of the present invention to overcome the disadvantages of the prior art and provide a method for economical production of precious metal jewelry and decorative objects having a unique and attractive appearance and lighter weight than similar items produced by casting.
In accordance with a preferred embodiment of the present invention, there is provided an item of jewelry or decorative item formed from gravity or low pressure. sintered spheres of precious metal having a unique and attractive appearance.
According to a preferred embodiment, there is provided an article of jewelry of attractive and original appearance, formed by sintered spherical particles of precious metal.
A feature of the present invention is to provide an item of jewelry or decorative object having a unique appearance, from sintered spherical particles of precious metal.
An advantage of the present invention is that the item of jewelry or decorative object has a unique appearance.
A further advantage of the present invention is that such items have lower density than similar items produced by casting, making items of jewelry lighter and more comfortable to wear.
A further advantage of the present invention is that such items are more economical to produce than similar items produced by casting, due to lower material requirements, since a larger volume is obtained per unit weight.
A further advantage of the present invention is that such items comprise spherical units, and are therefore devoid of sharp corners.
A further advantage of the present invention is that such items may be formed by combining spheres of various sizes, colors and materials, while retaining their individual characteristics.